Periodic acid

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Periodic acid is HIO₄ or H₅IO₆. The name is not derived from "period", but from "iodine": per-iodic acid (compare iodic acid, perchloric acid), and it should thus be pronounced per-iodic and not as in the usual meaning of periodic.

In dilute solution, periodic acid exists as H⁺ and IO₄⁻. When more concentrated, orthoperiodic acid, H₅IO₆, is formed. This can be obtained crystalline. Orthoperiodic acid can be dehydrated to metaperiodic acid, HIO₄. Further heating gives diiodine pentoxide (I₂O₅) and oxygen; apparently the anhydride 'diiodine heptoxide' does not exist in nature but can be formed synthetically.

Thus, two forms of periodates exist. One relating to the acid HIO_{4, the other relating to H5IO6. The former results in metaperiodates (meta- meaning less water) and the latter, orthoperiodates (ortho- meaning more water). Metaperiodates have solubilities and chemical properties similar to perchlorates (similar but larger ion size) though they are less oxidizing than perchlorates.}

_{Periodic acid is also used in organic chemistry for structural analysis. Periodic acid will cleave a vicinal diol into two aldehyde fragments. This can be useful in determining the structure of carbohydrates.}

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